The present invention relates to a knitting machine with a device for adjusting the stitch density and for offsetting the stitch cam with respect to adjacent knitting cams.
As is known, knitting machines, sock- and stocking-making machines and the like comprise a needle supporting element constituted, in circular machines, by a cylinder with a plurality of grooves defined along its directrices, in which the needles are accommodated and can slide axially; said needles have at least one heel protruding from said grooves to engage within paths defined by a plurality of shaped cams mounted on a supporting structure and arranged facing the needle supporting element. In circular machines with two needle beds there are two needle supporting elements, since a dial its arranged above the cylinder and has radial grooves in which other needles are accommodated and face the needles carried by the cylinder. The needles of the dial also have at least one heel which protrudes upwardly from the grooves of the dial and engages within paths defined by other cams mounted on a supporting structure arranged upwardly facing the dial. The relative motion between the supporting structures of the cams and the respective needle supporting elment causes the needles to follow the paths defined by the cams, moving the needles along the respective grooves to grip the thread fed by the thread guides and to form stitches. In circular machines said relative motion occurs about the axis of the machine, which coincides with the axis of the cylinder and with the axis of the dial.
Among the various knitting cams, the stitch cams are those which lower the needles of the cylinder or move the needles of the dial toward the axis of the dial after said needles have engaged the thread fed by a thread guide, casting off the previously formed stitches.
In order to adjust the knitting tightness, the stitch cams are controllably movable with respect to their supporting structure in a direction which is parallel to the axis of the needles which engage in each instance with said stitch cam. The stitch cams of the dial are movable in a radial direction with respect to the dial, while the stitch cams of the cylinder are movable in a direction which is parallel to the axis of the cylinder. By moving the stitch cams the length of the loops formed by the needles is changed and the obtainable stitch density is therefore varied.
For special knittings, in some case an anticipated or delayed offset of the stitch cams is required with respect to the needles. In cylinder and dial machines this operation is generally performed on the cams which act on the needles of the dial, offsetting the entire supporting structure of the dial cams with respect to the dial itself by a preset angle.
The operation of offsetting the supporting structure of the dial cams is generally performed manually or by means of mechanical actuators.
Besides obtaining the required change in the position of the stitch cams, offsetting the entire cam supporting structure also causes the offset of all the knitting cams, involving problems with regard to other kinds of knitting, for which a different position of the other knitting cams would be preferable. For example, in cylinder and dial machines the offset of the other knitting cams with respect to the original position may cause problems in knittings which require a transfer of the stitch from needles of the cylinder to needles of the dial or vice versa.
In multiple-feed machines, the offset of the entire knitting cam supporting structure furthermore causes the offset of the knitting cams of all the feeds and not only of the cams which act on the needles which must engage the thread at a specific feed and for which said offset is acutually required.